1. Field of the invention
The present invention concerns drying equipment comprising a battery of radiant heaters for drying a webform material moving past a radiant surface formed by said radiant heaters, a suction hood and a blower hood disposed on respective sides of the battery of radiant heaters in the direction of movement of the webform material to delimit a volume between the radiant surface, the surface of the webform material to be dried and the hoods.
2. Description of the prior art
Radiant heaters of the kind in question, often disposed in a battery, are designed to be fitted to a papermaking machine to dry the paper.
The thermal inertia of these systems makes it necessary to apply fire prevention measures.
There are two series of causes of fires.
Firstly, if the paper or the dry material comes into contact with the infrared system it catches fire. This can occur at any time and principally if the paper breaks and if particles of paper are detached from the moving surface.
There is also a risk of fire if the web is stopped under the infrared system.
In this case the paper catches fire because of the high temperature and the presence of oxygen.
Currently radiant heaters are provided with cells which detect the variation or energy caused by the occurrence of a flame and trigger a water spraying system. The response time of a system of this kind is approximately 0.2 second.
A response time of this magnitude represents very long distances in the case of high-speed machines where the rate of movement is in excess of 600 meters per minute. This effectively reduces the effectiveness of such systems.
What is more, spraying water pollutes the paper because droplets of water fall onto the paper after setting.
Existing prior art fire prevention systems, such as disclosed in FR 2 532 733, are always disposed externally of the battery of radiant heaters. These systems usually employ manifolds installed at the outside of one of the hoods about ten centimeters from the outside wall.
This type of system must be mounted and demounted independently of the battery of radiant heaters. The major drawback of this system is that, given the relatively small distance between the hood and the material to be dried, the steam and water is difficult to remove from the hood and some of the steam systematically impinges under pressure on the hood where it condenses so that droplets of water drop onto the paper or the material to be dried.
This method of fire prevention therefore raises serious problems concerning its effectiveness, which the system in accordance with the invention proposes to solve.